Heretofore, various solderless radiator tank to header joint arrangements have been used, as shown in FIGS. 1-4, and described in U.S. Pat. Nos. 4,485,867; 4,378,174; and 4,351,390; and British Pat. No. 699,032. Each of these prior art arrangements rely primarily on portions of the edges of their respective headers, or associated separate clips, being bent onto flanges formed on the respective tanks, to thereby compress an "O"-ring or other shaped resilient gasket between the tank and the header. Typically, headers are formed of a lighter gauge metal than tanks, or the tanks are formed of a suitable plastic with heavy gauge headers.